Hepatitis C virus (HCV) infects more than 170 million people worldwide and is the leading cause of chronic hepatitis, which can ultimately lead to end-stage liver cirrhosis and hepatocellular carcinoma. The standard treatment for HCV infection is currently pegylated interferon alpha (Peg-IFN) in combination with ribavirin (RBV). The goal of HCV therapy is to eliminate viral infection by obtaining a sustained viral response (SVR) as defined by having undetectable HCV-RNA in the blood after 6 months of antiviral treatment. Unfortunately, the current treatment is not effective in about 50% of subjects with genotype 1, and the side effects are significant. Thus, new antiviral targets and improved treatment strategies are needed (Pawlotsky, J. M., and J. G. McHutchison, 2004, Hepatitis C. Development of new drugs and clinical trials: promises and pitfalls. Summary of an AASLD hepatitis single topic conference, Chicago, Ill., Feb. 27-Mar. 1, 2003, Hepatology 39:554-67; Strader, et al., 2004, Diagnosis, management, and treatment of hepatitis C. Hepatology 39:1147-71).
The non-structural (NS) 3-4A protease is essential for HCV replication and a promising target for new anti-HCV therapy. VX-950, a potent and specific NS3-4A protease inhibitor demonstrated substantial antiviral activity in a phase 1b trial of subjects infected with HCV genotype 1 (Study VX04-950-101). The degree to which a subject responds to treatment and the rate at which viral rebound is observed could in part be due to genotypic differences in sensitivity to the protease inhibitor. The rapid replication rate of HCV, along with the poor fidelity of its polymerase, gives rise to an accumulation of mutations throughout its genome (Simmonds, P., 2004, Genetic diversity and evolution of hepatitis C virus—15 years on. J. Gen. Virol. 85:3173-88). The degree to which sequence variability in the protease region affects the catalytic efficiency of the enzyme or the binding of an inhibitor is not known. Additionally, the generation of numerous viral genomes with remarkable sequence variation presents potential problems of emerging drug resistant virus in subjects treated with antiviral therapy. Indeed, drug resistance against antiviral drugs, such as HIV protease inhibitors, is well documented (Johnson, et al., 2004, Top. HIV Med. 12:119-24). Drug resistant mutations have already been shown to develop in vitro in the presence of HCV protease inhibitors (Lin, et al., 2005, In vitro studies of cross-resistance mutations against two hepatitis C virus serine protease inhibitors, VX-950 and BILN 2061. J. Biol. Chem. 280:36784-36791; Lin, et al., 2004, In vitro resistance studies of hepatitis C virus serine protease inhibitors, VX-950 and BILN 2061: Structural analysis indicates different resistance mechanisms. J. Biol. Chem. 279:17508-17514; Lu, et al., 2004, Antimicrob. Agents Chemother. 48:2260-6; Trozzi, et al., 2003, In vitro selection and characterization of hepatitis C virus serine protease variants resistant to an active-site peptide inhibitor. J. Virol. 77:3669-79). Mutations resistant to the protease inhibitor BILN 2061 have been found at positions R155Q, A156T, and D168V/A/Y in the NS3 gene, but no mutations have yet been observed in the NS4 region or in the protease cleavage sites. A VX-950 resistance mutation has also been found in vitro at position A156S. Cross-resistant mutations against both VX-950 and BILN 2061 have also been shown to develop in vitro at position 156 (A156V/T) (Lin, et al., 2005, supra).
Accordingly, there exists a need in identifying mutated HCVs or other viruses that exhibit resistance to drugs or other therapies and in developing new viral therapeutics effective against these mutated viruses.